The present invention relates to an engine balancer apparatus for canceling vibration of a crankshaft.
As a conventional engine balancer apparatus, for example, Japanese Patent Laid-Open No. 8-100837 discloses a structure in which the axial center of a mass portion formed on a balancer shaft is set to coincide with the axial center of a crankshaft to transmit power from the rear side of the crankshaft to the balancer shaft.
In this prior art, while the crankshaft and balancer shaft are made of substantially the same materials (cast iron or the like), a cylinder block for axially supporting the crankshaft is made of a material (aluminum alloy or the like) different from that of the crankshaft and balancer shaft. Accordingly, due to a difference in thermal expansion, meshing of gears (or a chain and sprocket) for transmitting the power from the crankshaft to the balancer shaft degrades to sometimes cause backlash noise (or chain noise).
The present invention has been made in view of the above problem, and has as its object to provide an engine balancer apparatus for reducing backlash noise or the like which is generated when meshing of gears degrades due to a difference in thermal expansion.
In order to solve the above problem and achieve the object, according to the first aspect, a balancer shaft has a support portion made of a material having substantially the same coefficient of linear expansion as that of the balancer shaft and a crankshaft, and the support portion extends from a cylinder block position corresponding to the axis of the crankshaft. Thus, the material of the cylinder block from the axis of the crankshaft to the position for supporting the balancer shaft is replaced by the material of the support portion, and when thermal expansion occurs, the amount of thermal expansion from the axis of the crankshaft to the axis of the balancer shaft and the amount of thermal expansion of the support portion can be set to be substantially the same. Therefore, degradation in meshing of gears for transmitting power from the crankshaft to the balancer shaft is suppressed, thereby reducing backlash.
According to the second aspect, since power transmitting means for transmitting power from the crankshaft to the balancer shaft is arranged on the flywheel side of an engine, an adverse influence of the torsion of the crankshaft can be minimized.
According to the third aspect, since the crankshaft has a driving gear meshing with a driven gear of the balancer shaft, degradation in meshing of the gears is suppressed, thereby reducing the backlash noise.
According to the fourth aspect, since the gears of the crankshaft and the balancer shaft are formed by press-fitting annular members having gears onto circular disk members provided to the shafts, the gears can be built on the shafts easily.
According to the fifth aspect, a coefficient of linear expansion of one of the annular members with a diameter larger than that of corresponding one of the circular disk members is set substantially the same as a coefficient of linear expansion of the support portion of the balancer shaft. Thus, the material of the support portion can be set to match that of the annular members with a larger amount of expansion, thereby minimizing degradation in meshing of the gears.
According to the sixth aspect, the crankshaft and the balancer shaft are made of the same material. Thus, the amount of expansion of the support of the balance portion becomes substantially the same as those of the crankshaft and the balancer shaft. Degradation in meshing of the gears is thus suppressed, thereby reducing backlash noise.
According to the seventh aspect, the support portion of the balancer shaft forms a lubricant supply path to the balancer shaft. Thus, the lubricant supply path can be assured.
According to the eighth aspect, the apparatus is a secondary balancer apparatus for suppressing secondary vibration of a four-cylinder engine, and is arranged such that the center of a resultant force of balancer weights provided to the balancer shaft coincides with the center of a vibration system of the crankshaft. Therefore, secondary vibration can be canceled effectively.
According to the ninth aspect, in addition to the effect of aspect 1, the adverse influence of the torsion of the crankshaft can be minimized.
According to the tenth aspect, in addition to the effects of aspects 1 and 3, a lubricant supply path can be ensured.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.